Gun perforator



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GUN PERFORATOR IN1/EN TOR.

' ffm/w05 ,4. ,4A/0425111 Dec. 1l, 1956 T. A. ANDREW 2,773,424

GUN PERFORATOR Filed June 1.*195] 3 Sheets-Sheet 3 IN V EN TOR. f 75m/7.45 ,4. A'Nmaa/ BY frm. wfg

United States Patent O M GUN PERFoRAToR Thomas A. Andrew, Pasadena, Calif., assigner of onefonrth to Mordica O. Johnston, one-eighth to Mordica 0. Johnston, Jr., and one-eighth to Warren C. Johnston, all of Glendale, Calif.

Application June 1, 1951, Serial No. 229,506

13 Claims. (Cl. 89-1) The present invention relates to gun type perforators, and more particularly to perforators used' in well bores to penetrate casing disposed therein, as well as the surrounding formation.

Gun perforators are lowered into a well bore on a cable, or other suitable running-in string, the axes of the gun barrels running transversely of the axis'of the gun body and well bore. Inasmuch as the diameters of the well bores are comparatively small, the diameters of the gun bodies are also` correspondingly small, causing the vgun bores containing the bullets to be of comparatively short or restricted length. The short gun bore gives the bullet only a short distance in which to accelerate to casing penetrating velocity.

In order to develop the projectile velocity necessary for eiiicient penetration, restraining means of various types have been provided which either prevent the pressure developed by the burning propellant from acting on the bullet until a high magnitude of pressure has been produced, or which restrain the bullet from movement until propellent pressures of considerable magnitude have been developed.

One of the restraining means heretofore used comprises a rupturable disc placed between the propellant and the rear end of the bullet. This type of restraint leaves much to be desired, in that the rupturing disc fails in progressive stages and does not provide the restraining consistency desired. The disc expands into the gun bore, and while it appears on linal inspection to have completely sheared at the gun barrel diameter, preliminary failures may have occurred in the center during the rupturing procedure that may have caused the bullet to start its travel through the gun barrel bore at propellent pressures much lower than that needed, which decreases the velocity of the bullet leaving the gun bore and its effectiveness in perforating the well casing.

Where a projectile restraining means is used, vit is dicult to secure consistency of release and allow the bullet to have unimpeded travel down the gun bore once the initial pressure requirements developed by the propellant have been attained.

Heretofore, a bullet restraining means has involved the use of the ambient pressure or hydrostatic well pressure against the seal resting against the tip of the bullet, the pressure forcing the bullet against the propellant. Bullet movement commences when the burning propellent pressure equals the ambient pressure, but due to the large magnitude and variation of the ambient pressure under which a gun perforator must operate, depending upon the hydrostatic head of the well fluid surrounding the gun, this arrangement produces variations in the penetra*A tive force of the bullets red from the gun.

Gun perforators usually employ sealing elements to keep the external Well fluid from the bullet and barrel, and these elements must be removed by the bullet. This impedance tends to slow the bullet, robbing it of some of its penetrative ability.

In addition, the bullet may 2,773,424 Patented Dec. 11, 1956 ice also have to eject well iiuid from the gun barrel ahead of the sealing element and must also pierce the well lluid between the gun and the well casing. All of the foregoing factors.A tend to diminish the extent of subsequent penetration of the bullet into and through the well casing and the surrounding Well bore walls.

When a number of gun chambers are lired at the same time in a Well bore, they have heretofore reached their maximum explosive pressures at approximately the same instant, and, following ejection ofthe bullets, the well bore pressure is raised to such a great extent that damage might be done to the well bore walls, in some instances splitting the casing.

Accordingly, it is an object of the present invention to provide for a longer bullet travel in a well bore gun, despite the relatively small diameter of the gun and at the same time maintain a high mean pressure on the bullet during its longer travel.

Another object of the invention is to maintain a bullet in its initial position within the gun barrel by means of gas pressures until propellent pressures of considerable magnitude have been developed.

A further object of the invention is to force impeding elements in advance of the bullet, such as the barrel sealing element, any well liquid in the gun bore bearing against the sealing element and the well liquid between the gun and the well casing, from the bullet path before their initial locations are reached by the bullet, thereby insuring that the bullet will have an unimpeded trajectory, with maximum velocity and penetration into and through the well casing and the portions of the well bore surrounding it.

Yet another object of the invention is to minimize the danger of splitting or damaging well casing, or damaging other equipment in the well bore, by preventing a plurality of gun chambers fired at the same time from reaching their maximum pressure simultaneously, thereby greatly reducing well pressures attributable to the simultaneous firing of the propellants in the gun chambers.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown in the drawings accompanying and forming part of the present specication. These forms will now be described in detail, illustrating the general principles of the invention; but it is to be understood that such detail description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Fig. 1 is a side elevation of a gun body disposed in a well casing, into which it has been lowered on a cable, with bullets represented as having been fired from the gunv and penetrating the casing and the surrounding well bore;

Fig. 2 is an enlarged longitudinal section through a single gun barrel portion of the gun body;

Fig. 3 is a view similar to Fig. 2 of yet another embodiment of the invention;

Fig. 4 is a view similar to Fig. `2 of another embodiment of the invention;

Fig. 5 is a view similar to Fig. 2 of still another form of the invention;

Fig. 6 is a view similar to Fig. 2 of yet another embodiment of the invention;

Fig. 7 vis an enlarged fragmentary longitudinal sec-tion of a plurality of gun devices disposed in the gun body.

' In Fig. l, a typical gun body 10 is disclosed secured to an electric cable or line 11, by means of which it is lowered in a well casing. This body may have a plurality of gun barrels and bullets therein arranged in longitudinally spaced relation to one another, so as to be capable of firing a plurality of bullets through a well casing C to perforate the latter, the bullets rcontinuing on into the surrounding well bore.

As disclosed in Fig. 2, the gun body has a gun barrel 12 threaded thereinto, the axis of the barrel being disposed transversely or laterally of the longitudinal axis of the gun body. The barrel has a central gun bore 13 coaxially thereof which extends from the discharge end of the barrel rearwardly to an explosive chamber 14 provided in the gun body 10. Behind the explosive chamber is a rearward continuation 13a of the gun bore, being disposed coaxially of the latter.

The bullet P is disposed in the gun bore 13 and across the explosive chamber 14. The forward portion 15 of the bullet is disposed in the gun barrel bore in advance` of the chamber 14, the trailing portion 16 of the bullet being disposed in the gun bore 13a formed in the body behind the explosive chamber 14.

The explosive or propellent material 17 is provided in the explosive chamber 14 and surrounds a bullet P. In order to prevent leakage of well fluid through the threaded connection between the gun barrel 12 and gun body 10, and the leakage of gases resulting from firing the propellant 17, a suitable seal ring 18 is disposed in a circumferential groove 19 in the gun body 10 which is in scaling engagement with the periphery of the gun barrel 12. This seal ring 1S may be in the form of a rubber or rubberlike O ring, which is capable of effecting a seal between the gun barrel and gun body, preventing leakage in both directions therebetween. Leakage of the well iiuid is also prevented by a sealing disc 20 disposed across the mouth of the gun bore 13, or it could be provided by use of a sealing element 29a disposed in the gun bore and bearing against the tip 15 of the bullet, as illustrated in Fig. 3.

The explosive propellant 17 may be ignited in any suitable manner. As illustrated in Fig. 2, a propellant igniter 21 is disposed in a chamber 22 in the 1body communicable with the explosive chamber 14 through an interconnecting hole or passage 23. j When the igniter 21 is fired, either electrically or by percussion, the force of the explosion travels through the passage 23 to ignite `the propellant 17 contained in the explosive chamber 14. The force of this propellant 17 is at first incapable of acting upon the bullet to lire it through the gun bore 13. Instead, several preliminary actions first occur.

lt is to be noted that there is a small clearance space 24 provided between the periphery of the forward portion 15 of the bullet and the gun barrel 13, which establishes a flow path between the explosive chamber 14 and i the gun bore 13 in advance of the bullet P. Similarly, a small clearance space 25 is provided between the periphery of the rear 16 of the bullet P and the wall of the rear gun `bore 13a, which establishes-a flow path between the chamber 14 aud the rear face 26 of the bullet` and also with a comparatively small volume cavity 27, communieating with the end of the rear gun bore 13a and the clearance space 25 around the rear portion 16 of the bullet.

inasmuch as the propellant 17 surrounds the bullet P, there is no bullet area, except that of its periphery, exposed directly to the pressure developed in the chamber l-'i upon ignition of the propellant. lt is manifest that axial n'iovement of the bullet can be urged by pressures developed in the gun bore 13 ahead of the bullet P, or by pressures developed at the end of the rear gun bore portion 13a behind the bullet. Such pressures are obtainable in the present instance by allowing the propellent under pressure to pass through the ,clearance spaces 2a, 25' provided around the forward and rearward portion l5, 16 ofthe bullet P.

When the propellant 17 is ignited, the gas pressure is ineffective at first to eject thebullet through the gun bore 13. Instead, some gas under pressure first passes through the `small clearance ,space 24 around `lthe forward portion 15 of the bullet and into the gun bore 13, this pressure tending to force the bullet P rearwardly against the gun body. At the same time, the propellent gas under pressure has passed through the rear clearance space 25 into the small cavity 27, being capable of acting upon the rear end 26 of the bullet to urge it in a forward direction. As the pressure in the propellant chamber 14 increases, the burning propellent gases leak past the bullet through the forward clearance space 24 into the gun bore 13, exerting a pressure force against the sealing disc 20 and tending to force it from the gun barrel. Eventually, this pressure in the gun bore 13 equals and then exceeds the hydrostatic head of the well iiuid bearing upon the sealing disc 20 and tending to hold it in closed position across the gun barrel bore 13, When this condition arises, the gas pressure in the gun bore blows the sealing disc 20 out of the way. During all this time (actually of exceedingly short duration), the burning propellent gases are also moving through the small clearance space 25 around the rear 2d of the bullet into the rear cavity 27, and when this pressure exceeds the pressure in the gun bore acting against the nose `15 of the bullet, the bullet is shifted forwardly until its rear end 26 is disposed in the transverse plane of the burning propellant 17, which can now act with full force on the rear face 26 of the bullet and project the bullet at a high velocity through the gun bore.

The propellants 17 used in gun perforators develop their maximum pressures very quickly on ignition, requiring atime interval of a very short duration. In connection with the `foregoing description, it is to be realized that the time delay during which the burning gases are leaking past the bullet is very short, being suiicient to give the propellant 17 time to develop its maximum pressure, after which the rear 26 of the bullet is exposed to the full force of the propellent pressure as the bullet moves forwardly in the barrel 12. The time interval of delay before the bullet commences moving forward in the harrel may be adjusted, depending upon the extent of clearance 25 around the rear portion of the bullet and the volume of the cavity 27 communicating with the clearance space 25 around the bullet. The clearance space 24 around the forward portion of the bullet should be greater than that around the rear periphery of the bullet, to insure that the pressuredeveloped in the bore 13 in advance of the bullet will exceed that-developed behind the bullet at the first instant of detonation, to insure that the sealing disc 20 will be ejected before the bullet P commences its movement in the gun bore 13 to the point in which its rear face 26 is exposed to the maximum pressure of the explosive propellant .17.

The bullet, in moving through `the gun bore 13 and into the surrounding well casing, is unimpeded by any intervening elements. 1t is to be noted that before the bullet P begins advancing through the gun bore, the propellent gases in the gun bore in advance of the bullet `have ejected the sealing disc 20 from the gun barrel 12, and such propellent gases also cleared away the well bore liquids from the path of the bullet. ficcordingly` thc bullet P is free to travel through the gun bore 13, to strike the casing C with maximum velocity. As noted above, the time delay imposed by the propellant arrangement, and the manner in which the gases can leal; in both directions past the bullet P, insure the maximum pressure of the explosive propellant for action upon thc bullet, which will provide maximum velocity to the bullet.

Since the propellent gases in advance of the bullet have cleared away` the well bore liquids, the bullet travels through a passage unobstructed by solids or liquids. Accordingly, the bullet will be projected against the well casing with the same velocity, regardless of the magnitude of the hydrostatic or other pressure in the surrounding well bore.

IThe construction just described, in which the propellant `17 initially surrounds the bullet, allows a longer gun bore 13 to be used for-.the same diameter-of gun body and gives the bullet P maximum travel, allowing the explosive forces to act on the bullet for a longer period of time, thus insuring a greater penetrating velocity than has heretofore been obtainable for the same charge of propellant 17.

Another important advantage of this construction is that a substantial portion of the bullet travel is through the power chamber. Tests made by me indicate that the pressures maintained on the bullet during its travel in the power chamber are much higher than the pressures effective against the bullet when traversing the barrel. I am not certain of the reasons for this phenomenon, but believe that this difference in pressures may be due to a large pressure drop due to viscous flow of the gases or due to the bullet velocity exceeding the velocity of pressure propagation when traveling down the barrel. The velocity of pressure propagation increases with ncreases of temperature `of the gases. Therefore, in the above construction, a considerable amount of the bullet travel takes place in the powder chamber where the gases are hottest and where the gases are not required to travel down a barrel to be effective against the bullet.

It follows, therefore, that, in the present invention, not only has a longer bullet travel been obtained, but obtained in a manner to maintain a high mean pressure on the bullet during its travel. Consequently, a higher bullet speed has been obtained than would be obtained in a construction where the distance of bullet travel is the same as .in the instant case, but wherein the travel is entirely through a barrel.

The form of invention disclosed in Fig. 3 is essentially the same as that shown in Fig. 2. Instead of employing a propellant igniter 21, as in Fig. 2, the propellant 17 in the explosive chamber 14 in Fig. 3 .is ignited by an insulated conductor pin 30 capable of passing current through a fuse 31, for the purpose of igniting the propellant. In addition, instead of placing a sealing disc 20 at the mouth of the gun barrel, in Fig. 3 a sealing element 20a is placed Within the gun bore 13 against the nose of the bullet. In all other respects, the apparatus disclosed in Fig. 3 operates in the same manner as the device shown in Fig. 2. Before the bullet P commences moving in the barrel, the propellent gases leaking past the forward portion 15 of the bulletrfrom the firing chamber 14 will iirst eject the sealing element a and well fluid in advance thereof from the gun bore 13, the blast of gases also removing the well iluid between the gun body 10 and well casing C from the path of the bullet P before the latter .is projected out of the gun bore.

In the form of invention disclosed in Fig. 4, a cavity 32 is provided in the rear of the bullet P to furnish the required volume to be llled by the gases leaking in a rearward direction from the propellant chamber 14 along the periphery of the bullet and across its back face 26. By properly selecting the volume of this cavity 32, the rate at which the pressure increases behind the bullet can be determined with respect to the increase in pressure in advance of the bullet by the gases leaking through the forward clearance space 24; so as to furnish the necessary time delay that will insure ejection of the sealing element 20a and well lluid from the gun bore 13, as well as removing the well liquid from the space between the gun body 10 and the well casing C in alignment with the gun bore. This time Idelay will also be sufficient to insure the development of the maximum pressure by the burning gases in the chamber 14 for action upon the rear 26 of the bullet or projectile. If desired, the cavity 32 in the rear of the bullet P may be lled with an explosive powder 33. Ignition of the main explosive or propellant 17 develops pressure in the vpropellant chamber 14, which leaks through the rear clearance space to the rear of the bullet. As the pressure increases and reaches the proper magnitude,

the bullet P is ejected. Inasmuch `as the clearance space 2S around the rear portion 16 of the bullet is not great enough to sustain flame propagation, the explosive 33 in the cavity 32 will not ignite until the bullet has moved partially in the gun bore 13 to expose its rear portion 26 to the llame in the main propellant chamber 14. At this point, the explosive 33 in the cavity will ignite, the resultant gaseous pressure developed providing a booster action, which sustains the pressure as the bullet passes down through the barrel 13; so as to provide a higher average pressure during its ejection from the gun, with a resultant increase in velocity and penetrating force .into the casing C.

As disclosed in Fig. 5, the cavity 34, instead of being provided in the bullet P, may be provided in the gunl body 10 immediately to the rear of the bullet. This cavity 34 will have sufcient volume to provide the desired retarding in the movement of the bullet, by delaying the build-up of gas pressure behind the bullet, with respect to the gas pressure in advance of the bullet for a sutciently long time (which need only be a very small fraction of a second); to insure increase in the burning gas pressure inthe main chamber 14 to .its maximum value before the bullet is projected through the gun barrel 13.

Instead of merely providing clearance 24 around the periphery of the bullet P, the bullet may have a relatively tight t in the gun barrel bore 13, the amount of leakage past the bullet being obtainable through a shallow groove 35 (Fig. 5) formed in the wall of the gun bore 13, effecting intercommunication between the propellant chamber 14 and the gun bore 13.

The arrangement disclosed in Fig. 6 may be employed in connection with propellants 17 having an extremely fast burning rate. The back 26 of the bullet P is placed against the rear wal136 of the powder chamber 14, which shields the rear end 26 of the bullet and provides a restriction to the flow of the burning propellent gases as they tend to get behind the bullet. Pressure is built up by passing from the propellant chamber 14 and leaking between the bullet P and the back surface 36 of this chamber. This arrangement provides a comparatively short delay in time, which is, nevertheless, sufliciently appreciable to delay the movement of the bullet until the prescribed amount of gas pressure has been developed in the propellant chamber 14. As disclosed in Fig. 6, the gases under pressure can leak through the clearance space 24 around the forward portion 15 of the bullet and into the gun bore 13, for the purpose of ejecting the seal 20a, and Well fluid in the gun bore 13, and displacing ythe well liquid between the gun body 10 and wall of the well casing yC from the path of the bullet.

A plurality of gun devices is disclosed in Fig. 7 as being carried by the same gun body 10. It is desired to lire the bullets P in the gun devices substantially simultaneously, but to avoid the development of maximum propellent pressures simultaneously, which might tend to damage the well equipment and the well casing.

Each gun barrel assembly is essentially the same as that disclosed in Fig. 2, there being connecting channels or passages 40 extending from the back end of the rear gun bore 13a to the next lower propellant chamber 14. The propellant 17 in the upper chamber 14 is first ignited, following firing of the igniter 21, and it is this propellant which furnishes the high pressure gases that will travel through the interconnecting channel 40 to the next lower propellant chamber 14, to lire the propellant 17 in the latter. In the same manner, the propellant in the lower chamber develops gases under high pressure which can flow through the interconnecting channel 40 that leads to the next lower propellant chamber, and so on. Accordingly, it is apparent that the propellants 17 in the various chambers are tired in series.

rA time delay is introduced between the firing of an upper propellent charge 17 and a lower propellent charge.

Following firing of the upper propellent charge, the small clearance space 2S around the rear portion 16 of the upper bullet causes a delay in the build-up of pressure around this bullet and in the interconnecting channel 40 therebelow. Accordingly, the tiring of the next lower charge of propellant 17 is delayed, and, upon its firing, the building up of pressure in the next lower interconnecting channel 40 is delayed, through the necessity for the burning gases to pass through the comparatively small clearance space 25 around the rear 16 of the second bullet. This same retarding in the build-up of pressure continues in a series sequence down through the gun body, igniting all of the propellent charges in succession.

Accordingly, it is apparent that the propellent charges 17 will develop their maximum pressures in sequence to eject their associated projectiles P, there being a time delay between the maximum pressures developed between the upper chamber and the next lower chamber, from the next lower chamber to the one therebelow, and so forth throughout all of the chamberstin the gun body. Since the maximum pressures are not obtained simultaneously, the well bore pressures developed as a result of tiring all of the charges are at a substantially lesser magnitude than if all of the propellent charges were exploded simultaneously and developed their maximum pressures simultaneously. In thismanner, the decreasing of the effective pressures in the well bore minimizes the danger of damaging equipment in the well casing.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

l. Ina casing perforator: a gun body having a bore to receive a projectile; a projectile in said bore; said body having a propellent chamber communicable with said bore in advance of the rear face of the projectile when the projectile occupies its ring position in said bore; and means providing gas flow restricting passages between said chamber and the gun bore in advance of the projectile and behind the rear face of the projectile only when the projectile occupies its ring position in said bore.

2. In a casing perforator: a gun body having a bore to receive a projectile; a projectile in said bore; said body having a propellent chamber communicable with said bore in advance of the rear face of the projectile when the projectile occupies its tiring position in said bore; and means providing gas ow restricting passages between said chamber and the gun bore in advance of the projectile and behind the rear face of the projectile only when the projectile occupies its firing position in said bore, said passageto the gun bore in advance of the projectile being greater in area than the passage to the gun borebehind the projectile to provide a greater propellent gas pressure ahead of the projectile than behind the projectile.

3. In a casing perforator: a gun body having a bore to receive a projectile; a projectile in said bore; said body having a propellent chamber communicable with said bore in advance oit the rear face of the projectile when the projectile occupies its firing position in said bore; and means providing gas ow restricting passages between said charnber and the gun bore in advance of the projectile and behind the rear face of the projectile only when the projectile occupies its tiring position in said bore to provide a. greater propellent gas pressure ahead of the projectile than behind the projectile.

4. ln a casing perforator: a gun body having a bore to receive a projectile; a projectile in said bore; said body having a propellent chamber communicable with said bore in advance of the rear face of the projectile when the projectile occupies its tiring position in said bore; means providing gas ow `restricting passages between said. chamber and the gun bore in advance of the projectile and behindtthe rear face of the projectile only when the projectile occupies its tiring position in said bore; and means providing a chamber communicating withthe gun bore behind the projectile to initially provide less pressure in the gun bore behind the projectile than in advance of the projectile.

5. In a casing perforator: a gun body having a bore to receive a projectile; a projectile in said bore; said body having a chamber communicable with said bore and adapted to contain a propellant for ring the projectile from the bore; and means providing a ow restricting passage between said chamber and the gun bore in advance of the projectile only when the projectile occupies its tiring position in said gun bore, in order that the propellant can force substances from the gun bore in advance of the projectile.

6. In a casing perforator: a gun body having a bore to receive a projectile; a projectile in said bore; said body having a propellent chamber communicable with said bore in advance of the rear face of the projectile whenthe projectile occupies its firing position in said bore; means providing gas flow restricting passages between said chamber and gun bore in advance of the projectile and behind the rear face of the projectile only when the projectile occupies its firing position in said bore; and means providing a chamber in the gun body behind the projectile communicating with the gun bore behind the projectile to initially provide less pressure `in the gun bore behind the projectile than in advance of the projectile.

7. In a casing perforator:` a gun body having a bore -to receive a projectile; a projectile in said bore; said body having a propellent chamber communicable with said bore in advance of the rear face of the projectile when the projectile occupies its ring position in said bore; means providing gas ow restricting passages between said chamber and the gun bore in advance of the projectile and behind the rear face of the projectile only when the projectile occupies its firing position in said bore; means providing a second chamber communicating with the gun bore behind the projectile; and an explosive propellant in said second chamber.

8. In a casing perforator: a gun body having a bore to receive a projectile; a projectile in said bore; a propellent chamber surrounding said bore and communicating with said bore between the ends of the projectile when the projectile occupies its ring position in the bore; and means providing gas ow restricting passages between said chamber and the gun bore in advance of the projectile and behind the rear face of the projectile only when the projectile occupies its firing position in said bore.

9, In a casing perforator: a plurality of gun bodies connected together in superposed relation each having a bore to receive a projectile, each of said bores having a portion of enlarged diameter adjacent its rear end but spaced from said end, said enlargement constituting a propellent chamber, a projectile in said bore, said projectile bridging said propellent chamber when in its firing position, means forming a restricted passageway from said propellent chamber to the gun bore in front of said projectile only when said projectile is in its firing position, means forming a restricted passageway communicating between said propellent chamber and the gun bore behind said projectile when said projectile is in its firing position, and means providing a restricted passageway from the rear end of the gun bore of each of said gun bodies to the propellent chamber of the next lower gun body.

l0. In a casing perforator: a gun having a bore to receive a projectile, said bore having a portion of enlarged diameter adjacent its rear end, said enlargement constituting a propellent chamber a projectile in said bore, said projectile bridging said propellent chamber when in its firing position, means forming a restricted passage from said propellent chamber to the gun bore in front of said projectile only when said projectile is in its firing position, and means forming a restricted passageway communicating between said propellent chamber and the gun bore behind said projectile when said projectile is in its tiring position.

11. In a casing perforator: a gun having a bore to receive a projectile, said bore having a portion of enlarged diameter adjacent its rear end, said enlargement constituting a propellent chamber, a projectile in said bore, Said projectile bridging said propellent chamber when in its ring position, means forming a restricted passage from said propellent chamber to the gun bore in front of said projectile only when said projectile is in its tiring position, means forming a restricted passageway communicating between said propellent chamber and the gun bore behind said projectile when said projectile is in its firing position, the ratio of the total volume of the last men-tioned restricted passage and the space behind the projectile to the cross-sectional area of said restricted passage behing greater than the ratio of the total volume of the forwardly directed restricted passageway and the space in front of the projectile to the cross-sectional area of the forwardly directed restricted passage whereby the pressure will initially build up faster in front of the projectile than in the rear thereof to restrain said projectile against movement until the pressure in front thereof exceeds the hydrostatic Well pressure and clears the well uids from the bore and whereby the pressure behind the projectile subsequently exceeds the pressure in front thereof and forces the projectile outwardly through the cleared bore.

l2. In a casing perforator: a gun having a bore to receive `a projectile, said bore having a portion Iof enlarged diameter adjacent its rear end, said enlargement constituting a propellent chamber, a projectile in said bore, said projectile bridging said propellent chamber when in its tiring position, means forming a restricted passage from said propellent chamber to the gun bore in front of said projectile only when said projectile is in its firing position, means forming a restricted passageway communicating between said propellent chamber and the gun bore behind said projectile when said projectile is in its tiring position, the ratio of the total volume of the last mentioned restricted passage and the space behind the projectile to the cross-sectional area of said restricted passage being greater than the ratio of the total volume of the forwardly directed restricted passageway and the space in front of the projectile to the cross-sectional area of th-e forwardly directed restricted passage whereby the pressure will initially build up faster in front of the projectile than in the rear thereof to restrain said projectile against movement until the pressure in front thereof exceeds the hydrostatic well pressure and clears the well iiuids from the bore and whereby the pressure behind the projectile subsequently exceeds the pressure in front thereof and forces the projectile outwardly through the cleared bore, said projectile completely lling said bore after moving from its ring position to prevent further bypass of gases forwardly thereof.

13. In a casing perforator: a gun having a bore to receive a projectile, said bore having a portion of enlarged diameter adjacent its rear end, said enlargement con- .stituting a propellent chamber, a projectile in said bore, said projectile bridging said propellent chamber when in its firing position, means forming ,a restricted passage from said propellent chamber to the gun bore in front of said projectile only when said projectile is in its firing position, means forming a restricted passageway communicating between said propellent chamber and the gun bore behind said projectile when said projectile is in its tiring position, the ratio of the total volume of the last mentioned restricted passage and the space behind the projectile to the cross-sectional area of said restricted passage being greater than the ratio of the total volume of the forwardly directed restricted passageway and the space in front of the projectile to the cross-sectional area of the forwardly directed restricted passage whereby the pressure will. initially build up fas-ter in front of the projectile than in the rear thereof to restrain said projectile Vagainst movement until the pressure in front thereof exceeds the hydrostatic well pressure and clears the well uids from the bore and whereby the pressure behind the projectile subsequently exceeds the pressure in front thereof and forces the projectile outwardly through the cleared bore, said projectile completely lling said bore after moving from its ring position to prevent further bypass of gases forwardly thereof, a seal in said gun bore and engaging the nose of said projectile, said seal defining a gas space in front of said projectile connected to said forwardly directed restricted passage, said seal being adapted to be blown out with said well fluids ahead of said projectile.

References Cited in the le of this patent UNITED STATES PATENTS 428,311 Maxim May 20, 1890 695,809 Hawk Mar. 18, 1902 1,835,722 Rembert Dec. 8, 1931 1,856,022 Blacker Apr. 26, 1932 2,200,487 Calvert May 14, 1940 2,200,683 Schlumberger May 14, 1940 2,252,996 Tow Aug. 19, 1941 2,257,271 McCullough Sept. 30, 1941 2,262,925 Cole Nov. 18, 1941 2,264,450 Mounce Dec. 2, 1941 2,276,161 Cole Mar. 10, 1942 2,276,544 Miller Mar. 17, 1942 2,281,870 Cole May 5, 1942 2,292,670 Smith Aug. 11, 1942 2,317,238 Mennecier Apr. 20, 1943 2,349,666 McCullough May 23, 1944 2,423,453 Howe July 8, 1947 2,446,640 Davis Aug. 10, 1948 2,489,984 Shoemaker Nov. 29, 1949 2,517,560 Hambly Aug. 8, 1950 2,530,833 Martin Nov. 21, 1950 2,551,031

McCullough May 1, 1951 

